Derivative Instruments and Fair Value Measurements - Summary of Cash Settlements and Change in Fair Value of Commodity Derivatives (Detail) - Derivatives Not Designated as Hedging Instruments [Member] - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Derivatives Fair Value [Line Items] | |||
| Commodity derivative (loss) gain | $ (262) | $ (5,484) | $ 19,275 |
| Net Cash (Payment) Receipt on derivatives Settlements [Member] | |||
| Derivatives Fair Value [Line Items] | |||
| Commodity derivative (loss) gain | (4,359) | 6,132 | 52,489 |
| Non-Cash Fair Value Gain (Loss) on Derivatives [Member] | |||
| Derivatives Fair Value [Line Items] | |||
| Commodity derivative (loss) gain | $ 4,097 | $ (11,616) | $ (33,214) |